Deformation twinning in nanocrystalline metals

Deformation twins have been oberved in nanocrystalline Al processed by cryogenic ball-milling and in nanocrystalline Cu processed by high-pressure torsion at a very low strain rate. They were formed by partial dislocations emitted from grain boundaries. This paper first reviews experimental evidences and atomistic simulation results on deformation twinning and partial dislocation emissions from grain boundaries and then discusses recent analytical models on the nucleation and growth of deformation twins. These models are compared with experimental results to establish their validity and limitations. This paper was presented at the International Symposium of Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee on October 18–20, 2004 in Columbus, OH.